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UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS
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GCE Ordinary Level
MARK SCHEME for the October/November 2010 question paper
for the guidance of teachers
5070 CHEMISTRY
5070/31
Paper 3 (Practical Test), maximum raw mark 40
This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of
the examination. It shows the basis on which Examiners were instructed to award marks. It does not
indicate the details of the discussions that took place at an Examiners’ meeting before marking began,
which would have considered the acceptability of alternative answers.
Mark schemes must be read in conjunction with the question papers and the report on the
examination.
•
CIE will not enter into discussions or correspondence in connection with these mark schemes.
CIE is publishing the mark schemes for the October/November 2010 question papers for most IGCSE,
GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level
syllabuses.
Page 2
1
Mark Scheme: Teachers’ version
GCE O LEVEL – October/November 2010
Syllabus
5070
(a) Titration
Paper
31
[12]
Accuracy
8 marks
For the two best titres give:
4 marks for a value within 0.2 cm3 of supervisor
2 marks for a value within 0.3 cm3 of supervisor
1 mark for a value within 0.4 cm3 of supervisor
Concordance
3 marks
Give:
3 marks if all the ticked values are within 0.2 cm3
2 marks if all the ticked values are within 0.3 cm3
1 mark if all the ticked values are within 0.4 cm3
Average
1 mark
Give 1 mark if the candidate calculates a correct average (error not greater than 0.05) of all
his ticked values.
Assuming a 25 cm3 pipette and a titre of 24.8 cm3.
(b) concentration of hydrogen ions in P
=
[2]
25 × 0.1
(1)
24.8
= 0.101 (1)
Answers should be correct to + or – 1 in the third significant figure.
(c) moles of hydrogen ions in 10000 dm3 of contaminated water
[1]
= 0.101 × 10000 (1)
= 1010
(d) mass of calcium carbonate needed to neutralise the acid
= 1010/2 (1)
= 1010 × 100 (1)
= 50500 g
© UCLES 2010
[2]
Page 3
2
Mark Scheme: Teachers’ version
GCE O LEVEL – October/November 2010
R is aluminium
Syllabus
5070
S is potassium nitrate
Test
Notes
General points
For ppt
allow solid, suspension, powder
For gases
Name of gas requires test to be at least partially correct.
Effervesces = bubbles = gas vigorously evolved (but not just gas evolved)
Solutions
Colourless not equivalent to clear, clear not equivalent to colourless
Solution R
Test 1
effervescence
pops with a lighted splint
hydrogen
(1)
(1)
(1)
Test 2
white ppt
soluble in excess
colourless solution
(1)
(1)
(1)
Test 3
white ppt
insoluble in excess
(1)
(1)
Test 4
(a) effervescence
pops with a lighted splint
hydrogen
(1)
(1)
(1)
(b) white ppt
soluble in excess
colourless solution
(1)
(1)
(1)
Test 5
(a) no reaction
(1)
(b) red/brown solid formed
blue colour fades
effervescence
(1)
(1)
(1)
© UCLES 2010
Paper
31
Page 4
Mark Scheme: Teachers’ version
GCE O LEVEL – October/November 2010
Syllabus
5070
Paper
31
Test 6
(a) liquid turns green
(1) accept green-yellow or colourless
(b) green ppt
insoluble in excess
(1) black/dirty green ppt
(1)
Test 7
turns litmus blue
(1)
ammonia
(1)
[20]
R is aluminium/Al (ppt must dissolve in test 2 and ppt must not dissolve in test 3) (1)
R is acting as a reducing agent (any green in test 6(a) or green/black in test 6(b) (1)
S contains nitrate or NO3– (test 7 correct – allow alkaline gas, smell of ammonia) (1)
Note: 26 marking points, maximum 23.
© UCLES 2010
[3]